Context-aware distributed firewall

ABSTRACT

A context-aware distributed firewall scheme is provided. A firewall engine tasked to provide firewall protection for a set of network addresses applies a reduced set of firewall rules that are relevant to the set of addresses associated with the machine. A hypervisor implements a search structure that allows each virtual machine&#39;s filter to quickly identify relevant rules from all of the received rules. The search structure is constructed as a binary prefix tree, each node corresponding to an IP CIDR (Classless Inter-Domain Routing) block. A query for relevant rules traverses nodes of the search structure according to a queried IP address and collect all rules that are associated with the traversed nodes.

CLAIM OF BENEFIT TO PRIOR APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 15/633,384, filed Jun. 26, 2017, now published asU.S. Patent Publication 2017/0366504. U.S. patent application Ser. No.15/633,384 is a continuation of U.S. patent application Ser. No.14/558,561, filed Dec. 2, 2014, now issued as U.S. Pat. No. 9,692,727.U.S. patent application Ser. No. 15/633,384, now published as U.S.Patent Publication 2017/0366504 and U.S. patent application Ser. No.14/558,561, now issued as U.S. Pat. No. 9,692,727 are incorporatedherein by reference.

BACKGROUND

In a Software Defined Datacenter (SDDC) environment, distributed networkfirewall is replacing traditional firewall in order to meet newrequirements of granularity and scalability. Typically, a firewallcontroller is deployed on each hypervisor to protect the virtualmachines (VMs) running on the hypervisor, and a centralized managementcomponent distributes firewall rules to all firewall controllers in theSDDC. Often, every firewall controller receives a large set of rulestargeting at the entire datacenter. The firewall controller then appliesall the rules to every protected VM in the datacenter. FIG. 1illustrates a distributed firewall scheme in a datacenter 100 in whichthe complete set of firewall rules is applied to every VM. In thisscenario, the large rule set can cause significant burden to firewallengine because every single network packet has to be inspected againstthe entire rule set. In addition, it also consumes large amount ofmemory because the rule set is replicated to every protected VM.

SUMMARY

Some embodiments of the invention provides a context-aware distributedfirewall scheme in which a firewall engine tasked to provide firewallprotection for a set of network addresses applies a reduced set offirewall rules that are relevant to the set of addresses associated withthe machine. In some embodiments, firewall controllers are implementedby hypervisors or virtualization software running on host machines, andthe network addresses protected by the firewall controllers correspondto the network addresses of the VMs being hosted by the hypervisors.Some or all of these firewall controllers are part of the hypervisorsthat allow host machines to operate VMs. The firewall controllers inturn protect those VMs by providing rules that are relevant to thenetwork addresses of these VMs.

In some embodiments, each host machine receives firewall configurationmessages regarding all rules in the datacenter. However, thehypervisor/firewall controller of the host machine identifies only therelevant rules for each of its VMs such that the hypervisor would onlyhave to apply the identified relevant rules to check against theincoming packets. In some embodiments, the hypervisor implements asearch structure that allows each VM's filter to quickly identify therelevant rules from all of the received rules.

In some embodiments, the search structure is for identification ofqualifying rules (rules specified by IP CIDR blocks) that are relevantto a VM or a set of VMs. Each node of the search structure correspondsto an IP CIDR block. A rule is associated with a node if the rule'ssource or destination address field specifies the node's IP CIDR block.If multiple rules specify the same IP CIDR block in their addressfields, the node that corresponds to the IP CIDR block would beassociated with the multiple rules. In some embodiments, the searchstructure is constructed as a binary prefix tree.

To use the search structure for identifying the relevant rules for a VM,some embodiments uses the IP address of the VM to query the searchstructure. The query traverses nodes of the search structure and collectall rules that are associated with the traversed nodes. A node in thesearch structure will be traversed if (i) its CIDR block encompasses thequeried IP address and (ii) all of its ancestor nodes are alsotraversed.

The preceding Summary is intended to serve as a brief introduction tosome embodiments of the invention. It is not meant to be an introductionor overview of all inventive subject matter disclosed in this document.The Detailed Description that follows and the Drawings that are referredto in the Detailed Description will further describe the embodimentsdescribed in the Summary as well as other embodiments. Accordingly, tounderstand all the embodiments described by this document, a full reviewof the Summary, Detailed Description and the Drawings is needed.Moreover, the claimed subject matters are not to be limited by theillustrative details in the Summary, Detailed Description and theDrawings, but rather are to be defined by the appended claims, becausethe claimed subject matters can be embodied in other specific formswithout departing from the spirit of the subject matters.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 illustrates a distributed firewall scheme in a datacenter inwhich the complete set of firewall rules is applied to every VM.

FIG. 2 illustrates a distributed firewall architecture in which eachdistributed firewall controller uses only a reduced, relevant rule setfor the network addresses that it is protecting.

FIG. 3 illustrates context-aware firewall controllers that areimplemented in hypervisors for protecting the VMs that are operating onthose hypervisors.

FIG. 4 illustrates a hypervisor that receive the complete set offirewall rules from a network manager and identifies rules that arerelevant to each VMs of the hypervisor.

FIG. 5 conceptually illustrates a process for performing firewallfiltering operations by identifying and applying only relevant rules.

FIG. 6 illustrates a firewall rule in which each rule has only IP CIDRblocks as source and destination addresses.

FIG. 7 illustrates a search structure for efficiently identifyingrelevant rules from the qualified rules in the set.

FIG. 8 illustrates using a search tree to identify relevant rules forseveral example IP addresses.

FIG. 9 conceptually illustrates a process for using a search tree offirewall rules to identify qualified rules relevant to an IP address.

FIG. 10 conceptually illustrates a process for constructing and updatinga prefix tree search structure for identifying relevant rules to a localfirewall controller.

FIG. 11 illustrates an example host machine that is operatingvirtualization software for hosting virtual machines.

FIG. 12 conceptually illustrates an electronic system with which someembodiments of the invention are implemented.

DETAILED DESCRIPTION

In the following description, numerous details are set forth for thepurpose of explanation. However, one of ordinary skill in the art willrealize that the invention may be practiced without the use of thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form in order not to obscure the descriptionof the invention with unnecessary detail.

Some embodiments of the invention provides a context-aware distributedfirewall scheme in which a firewall engine tasked to provide firewallprotection for a set of network addresses apply a reduced set offirewall rules that are relevant to the set of addresses associated withthe machine. For some embodiments, this invention solves the challengescaused by large rule set by reducing the rules being loaded on each VMbased on network addresses of the VM. In some embodiments, the networkaddresses of a VM are used to determine all relevant firewall rules forthe VM.

In some embodiments, when a VM is connected to the network, it presentsitself with one or more valid network addresses in order to participatein network communication. The hypervisor detects the network addressesof the VM, then identifies firewall rules whose defined networkaddresses are a superset of the VM's network addresses. These identifiedrules are the firewall rules that are relevant to the VM. These rulesare applied to the VM, and the firewall engine would use only theserules to inspect the network traffic of the VM. Typically, the totalnumber of firewall rules for a datacenter can be quite big, from therange of tens of thousands to a hundred of thousands. However, thenumber of firewall rules for a single VM is quite small, no more than ahundred. Thus, distributed firewall based on the reduced, relevant ruleset can achieve significant savings in memory and in processing time.

In some embodiments, a firewall engine in a hypervisor stores thenetwork addresses of all firewall rules in a trie-like data structure.After detecting the network addresses of a new VM, the firewall enginelooks up the rule trie and finds all rules whose addresses are asuperset of the VM's network addresses. It then applies these rules tothe VM. The firewall engine will use only the rules attached to the VMto inspect network traffic for that VM.

Several more detailed embodiments of the invention are described below.Section I describes system architecture for implementing thecontext-aware distributed firewall scheme. Section II describes a searchstructure that facilitates the identification of relevant rules for alocal firewall controller. Section III describes an example computingdevice that serve as a host machine of VMs. Finally, section IVdescribes an electronic system with which some embodiments of theinvention are implemented.

I. Architecture

FIG. 2 illustrates a distributed firewall architecture in which eachdistributed firewall controller uses only a reduced, relevant rule setfor the network addresses that it is protecting. Some embodiments referto these distributed firewall controllers as being context aware,because each of these firewall controllers is aware of the networkaddresses that it has to protect and in turn use only the rule sets thatare relevant to the network addresses that it is aware of.

The figure illustrates a datacenter 200 that implements a distributedfirewall scheme. As illustrated, the datacenter 200 employs multipledistributed (or local) firewall controllers 211-219. Each of thesefirewall controllers is tasked to protect one or more network addresses(i.e., the network node that are associated with these networkaddresses). As illustrated, the firewall controller 211 is tasked toprotect network addresses A, B, and C and the firewall controller 219 istasked to protect network addresses X, Y, and Z.

The datacenter 200 has a complete set of firewall rules 205. Each rulehas a source field and a destination field. Each source/destinationfield specifies a network address, a range of network addresses (such asa CIDR block), or collection of network addresses (such as a container).A packet having a source address and a destination address thatrespectively falls within the source field and the destination field ofa rule is subject to the specified action/requirement of the rule.

These rules are for protecting all network addresses in the datacenter200 (e.g., all VMs running on all host machines of the datacenter). Asillustrated, some of the rules are applicable to the addresses protectedby the firewall controller 211 (addresses A, B, and C are protected byrules 1, 2, 3, 1001, and 1002), while some of the rules are applicableto the addresses protected by the firewall controller 219 (addresses X,Y, and Z are protected by rules 1001, 1002, 2001, and 2002). However,unlike the distributed firewall scheme of FIG. 1 in which each firewallcontroller has to inspect the entire rule set of the datacenter 100,each firewall controller in the datacenter 200 of FIG. 2 iscontext-aware and only inspects a relevant subset of the rule set 205for the network addresses that it is protecting.

As illustrated, the context-aware firewall controller 211 provides onlysubsets 221, 222, and 223 of the rules for addresses A, B, and Crespectively, Consequently, the firewall of address A inspects onlyrules 1, 2, and 1001, the firewall of address B inspects only rules 1,3, and 1002, the firewall of address C inspects only 2 and 3, etc.Likewise, the context-aware firewall controller 219 provides onlysubsets 227, 228, and 229 of the rules for addresses X, Y, and Zrespectively. Consequently, the firewall of address X inspects onlyrules 1001, 2001, and 2002, the firewall of address Y inspects onlyrules 1002 and 2001, the firewall of address Z inspects only rules 2002,etc.

In some embodiments, the firewall controllers 211-219 are implemented byhypervisors or virtualization software running on host machines, and thenetwork addresses protected by the firewall controllers correspond tothe network addresses of the VMs being hosted by the hypervisors. Someor all of these firewall controllers part of the hypervisors that allowhost machines to operate VMs. The firewall controllers in turn protectthose VMs by providing rules that are relevant to the network addressesof these VMs. For some embodiments, FIG. 3 illustrates context-awarefirewall controllers that are implemented in hypervisors for protectingthe VMs that are operating on those hypervisors.

FIG. 3 illustrates a datacenter 300 that has a set of centralizedfirewall rules 305 for protecting the entire datacenter. The centralizedfirewall rules 305 are maintained by a network manager 310 of thedatacenter 300. Several host machines 311-319 are situated in thedatacenter 300. The network manager 310 and the host machines 311-319are interconnected by a physical network infrastructure 390, whichallows the network manager to send control plane messages to each of thehost machines, including firewall configuration messages. The hostmachines 311-319 in the datacenter 300 operate VMs A through Z, and thecentralized firewall rules 305 includes rules for protecting all ofthose VMs.

Each host machine is operating hypervisor or virtualization softwarethat allows the host machine to host one or more VMs. As illustrated,the host machine 311 is hosting VMs A, B, and C, the host machine 312 ishosting VMs D, E, and F, and the host machine 319 is hosting VMs X, Y,and Z. The virtualization software of each host machine also operates a(local copy of) distributed firewall controller for protecting the VMsthat it is hosting. Each hypervisor performs firewall operation for eachof its VMs based on a reduced set of rules that is relevant to the VM.For example, the virtualization software of the host machine 311 onlyuse firewall rules that are relevant to VM A for VM A, firewall rulesthat are relevant to VM B for VM B, etc. By not having to search throughirrelevant firewall rules, each hypervisor-implemented distributedfirewall controller is able to achieve significant savings in packetprocessing time and memory usage.

Different embodiments use different methods for ensuring that the onlythe relevant rules are considered by each distributed firewallcontroller. In some other embodiments, the network manager of thedatacenter learns which VMs are being protected by a particulardistributed firewall controller. The network manager then identifies therelevant rules for those VMs and sends firewall configuration messagescontaining only the identified relevant rules to the particulardistributed firewall controller. Each host machine therefore only storesthe relevant rules for the VMs that it is hosting.

In some embodiments, each host machine receives firewall configurationmessages regarding all rules in the datacenter. As illustrated in FIG.3, each host machine 311-319 receives all rules in the datacenterfirewall rules 305 from the network manager 310. However, thehypervisor/firewall controller of the host machine identifies only therelevant rules for each of its VMs such that the hypervisor would onlyhave to apply the identified relevant rules to check against theincoming packets. FIG. 4 illustrates a hypervisor that receive thecomplete set of firewall rules from a network manager and identifiesrules that are relevant to each VMs of the hypervisor.

As illustrated, the hypervisor for each host machine in the datacenter300 includes a local firewall controller, a search structure, and a setof filters for its VMs. For example, the host machine 311 runs ahypervisor that includes a local firewall controller 421, a searchstructure 431, and a set filters 441-443 for its VMs A, B, and C,respectively. The local firewall controller 421 receives control planemessages from the network manager 310. The control plane messagesinclude the firewall rules for the entire datacenter. The local firewallcontroller 421 in turn uses the received firewall rules to construct thesearch structure 431 that includes the entire firewall rule set of thedatacenter 300. Each filter of the hypervisor 311 (filters 441-443) inturn uses the search structure 431 to query the rules that are relevantto the IP addresses of its corresponding VM. The relevant rules of a VMbeing those whose source or destination addresses encompass or areidentical to the IP address of the VM.

In some embodiments, a hypervisor creates a filter as a logical networkintrospection entity when a virtual NIC (network interface controller)of a protected VM is connected to a L2 virtual switch of the hypervisor.This filter contains a set of firewall rules and allows the firewallcontroller to inspect all network packets passing through the virtualNIC against the rules. After receiving a new firewall configurationmessage from the network manager, the hypervisor programs the filter ofall protected VMs with new rules. Rather than passing all received rulesto every applicable filter in the kernel, the hypervisor in someembodiments implements a search structure (such as the search structure431 for the hypervisor 311) that allows each VM's filter to quicklyidentify the relevant rules from all of the received rules. Searchstructures for identifying relevant rules will be further describedbelow in Section II.

FIG. 5 conceptually illustrates a process 500 for performing firewallfiltering operations by identifying and applying only relevant rules.The process is performed by hypervisors running on host machines in someembodiments. Specifically, in some embodiments, the process 500 isperformed by a filter module for a VM.

The process starts when it receives (at 510) a packet for the VM. Theprocess then uses (at 520) the firewall rules search structure toidentify rules that are relevant to the VM based on the IP address ofthe VM. In some embodiments, the filter caches the relevant rules andonly uses the firewall rules search structure to update its cached ruleswhen the firewall rules have been updated, e.g., when the hypervisorreceives a firewall configuration message from the network controller.

The process then identifies (at 530) the source and destination addressfields of the received packet and perform (at 540) firewall operationson the incoming packet (e.g., to block, to allow, etc.) by applying therelevant rules of VM. In some embodiments, the process goes through therelevant rules and applies those having source and destination fieldsthat respectively encompass the source and destination fields of theincoming packet. The process 500 then ends.

II. Search Structure

As mentioned, an address field of a firewall rule can specify a networkaddress, a range of network addresses, or collection of networkaddresses. Different embodiments use different types of searchstructures that are optimized toward different types of address fields.

For example, some embodiments use container-based search structures thatare optimized toward address fields that are specified as containers ofnetwork addresses. U.S. patent application Ser. No. 14/295,553 titled“Efficient Packet Classification for Dynamic Containers” filed on Jun.4, 2014, now issued as U.S. Pat. No. 9,774,707, describes a searchstructure for rules that use containers to specify source and/ordestination addresses. U.S. patent application Ser. No. 14/295,553, nowissued as U.S. Pat. No. 9,774,707, is hereby incorporated by reference.

In some embodiments, the firewall rules use IP CIDR blocks to specifythe source and destination addresses, and the local firewall controllersin the hypervisors use search structures that are optimized for findingrelevant rules among rules that use IP CIDR blocks to specify source anddestination addresses. CIDR (Classless Inter-Domain Routing) notation isa compact representation of an IP address and its associated routingprefix. The notation is constructed from the IP address and the prefixsize, the latter being equivalent to the number of leading 1 bits in therouting prefix mask. The IP address is expressed according to thestandards of IPv4 or IPv6. It is followed by a separator character, theslash (‘/’) character, and the prefix size expressed as a decimalnumber. The address may denote a single, distinct interface address orthe beginning address of an entire network. For example, the IP CIDRblock 192.168.100.0/24 specifies a routing prefix 192.168.100.0 and asubnet mask 255.255.255.0 (i.e., 24 leading 1-bits). In other words, thenotation 192.168.100.0/24 represents a subnet that includes a range ofaddress from 192.168.100.0 through 192.168.100.255. For someembodiments, an individual IP address can be regarded as a /32 CIDRblock (i.e., having 1-bits for the entire subnet mask).

In some embodiments, a rule is regarded as being irrelevant to a VM ifboth source and destination addresses of the rule is defined as IP CIDRblocks but the IP address of the VM does not fall in either IP CIDRblocks. Any IP packet from or to the VM will not match the irrelevantrule because both the source and destination addresses of the packetwill not match that of the rule. Conversely, if the IP address of a VMfalls in either source or destination IP CIDR block of a rule, the ruleis relevant to the VM and thus has to be used to examine packets from orto the VM. The local firewall controller in some embodiments thereforefinds all rules that are relevant to a VM based on this criterion.

Some embodiments classify firewall rules into two categories: qualifiedrules and non-qualified rules. If both source and destination address ofa rule are defined as IP CIDR blocks (or a set of IP CIDR blocks), andthe IP CIDR blocks are neither broadcasting nor multicasting addresses,the rule is qualified. All other rules are non-qualified rules.Non-qualified rules typically fall into the following categories:

-   -   Either or both addresses of the rule are not defined, meaning        they are wild-card address.    -   Either or both addresses of the rule have negation flag.    -   Either or both addresses of the rule are broadcasting or        multicasting address.    -   Either or both addresses of the rule is non-IP address.

In some embodiments, all non-qualified rules are used by a localfirewall controller of the hypervisor regardless of IP addresses of theprotected VMs. In other words, the local firewall controller in someembodiments considers all non-qualified rules as relevant rulesregardless of the IP addresses of the VMs that are being protected.However, a firewall system typically has far more qualified rules thannon-qualified rules. A local firewall controller in some embodimentstherefore uses a search structure for efficiently finding the relevantrules that are qualified.

FIG. 6 illustrates an example firewall rule set 600. The firewall ruleset 600 includes qualified rules 601-608 (rules with IDs 1 through 8)that each has only IP CIDR blocks as source and destination addresses.For example, the rule 601 specifies the IP CIDR block 192.168.17.0/24 asits source address and the CIDR block 192.168.101.0/28 as itsdestination address. The rule 606 specifies IP addresses 192.168.17.5and 192.168.17.247 as source address and destination addressrespectively, but these are equivalent to CIDR blocks having 32 1's inits subnet mask (i.e., 192.168.17.5/32 and 192.168.17.247/32).

The IP CIDR blocks of the firewall rule sets 600 all belong to a subnet192.0.0.0/8. The IP CIDR blocks used by the rules in the qualified rulesets are subsets or subnets of 192.0.0.0/8. FIG. 6 also conceptuallyillustrates the logical relationships between the some of the differentIP CIDRs specified by the rules in the set 600. For example, the VM192.168.101.2 is in a subnet 192.168.101.0/28, which is the IP CIDR usedby the rule 601, 605, and 607. The subnet 192.168.101.0/28 is in turn asubset of the subnet 192.168.0.0/16, which is used by the rule 602.Consequently, the rules 601, 602, 605, and 607 are the relevantqualifying firewall rules for the VM having IP address 192.168.101.2.

FIG. 7 illustrates a search structure 700 for efficiently identifyingrelevant rules from the qualified rules in the set 600. The searchstructure 700 includes nodes 701-714. Each node corresponds to an IPCIDR block. A rule is associated with a node if the rule's source ordestination address field specifies the node's IP CIDR block. If two (ormore) rules both specifies the same IP CIDR block in their addressfields, the node that corresponds to the IP CIDR block would beassociated with both rules (e.g., by a linked list that includes bothrules). For example, the rules 601 (rule ID 1), 605 (rule ID 5), and 607(rule ID 7) all specify the IP CIDR block 192.168.101.0/28 as a sourceor destination address. In the prefix tree 700, the node 708 correspondsto the IP CIDR block 192.168.101.0/28, and thus the node 708 isassociated with the rules with IDs 1, 5, and 7. As illustrated, thenodes 702, 703, 704, 705, 708, 710, 711, 712, 713, and 714 are all nodesthat are associated with one or more qualified rules from the set 600.

The search structure 700 is constructed as a binary prefix tree or trie(i.e., a Patricia tree with radix 2), in which each node has at most twochild nodes. In some embodiments, the CIDR block of each child node is asubnet of the CIDR of the parent node. For example, the node 707 and 711are child nodes of the node 706. The CIDR block of the node 707(192.168.64.0/18) and the CIDR block of the node 711 (192.168.17.0/24)are both subnets encompassed by the CIDR block of the node 706(192.168.0.0/17). Consequently, any node in the search tree 700corresponds to a IP CIDR block that encompass all of IP CIR blocks ofits offspring nodes (e.g., the CIDR block (192.0.0.0/8) of the root node701 encompasses the CIDR blocks of all other nodes 702-713 in the prefixtree.)

In some embodiments, the IP CIDR block of each node can be expressed asa prefix binary string whose length is determined by the ‘/’ notation.For example, the CIDR 192.168.0.0/17 of the node 706 can be expressed asa 17 bit long prefix binary string 11000000101010000. Each child node ofthe node can in turn be arrived at by appending the prefix string of theparent node with a suffix substring. For example, the CIDR of the node707 (192.168.64.0/18) can be arrived at by appending a 1-bit suffixsubstring ‘1’ to the prefix string of the parent node 706 (i.e.,11000000101010000_1). The CIDR of the other child node 711(192.168.17.0/24) can be arrived at by appending a 7-bit suffixsubstring ‘0010001’ to the prefix binary string of the parent node 706(i.e., 11000000101010000_0010001). The appended string for a child nodein turns becomes the prefix binary string of the child node, which inturn can append a suffix substring to arrive at a prefix string of agrand-child node, and so forth. Consequently, except for the root node701, every node in the search tree 700 is associated with a suffixsubstring. For example, the node 701 is associated with a 8-bit suffixsubstring 1100000, the node 705 is associated with a 8-bit suffixsubstring 10101000, the node 706 is associated with 1-bit suffixsubstring 0, the node 711 is associated with a 7-bit suffix substring0010001, and the node 712 is associated with a 8-bit suffix substring11110111. The binary string or the CIDR block of each node can bederived by appending the suffix substrings of all of its ancestor nodesto the root node. For example, the CIDR block 192.168.17.247 of the node712 is the appended result of all the suffix substrings of nodes 701,705, 706, 711, and 712 (1100000_10101000_0_0010001_11110111).

For a node having two child nodes in the search tree, one child node ison a ‘1’ path and the other child node is on a ‘0’ path. More precisely,in some embodiments, one child node is associated with a suffixsubstring that starts with ‘0’ and the other child node is associatedwith a suffix substring that starts with ‘1’. For example, the node 706has a ‘1’ child node 707 associated with the suffix substring ‘1’ and a‘0’ child node 711 associated with the suffix substring ‘0010001’. Whentraversing the search tree for a particular IP address or CIDR block,the traversal would take the ‘1’ path if the suffix string of the ‘1’path matches corresponding bits in the particular IP address or CIDRblock. Likewise, the traversal would take the ‘0’ path if the suffixstring of the ‘0’ path matches the corresponding bits of the particularIP address or CIDR block. If neither the ‘1’ path or the ‘0’ path has amatching suffix string for the IP address or CIDR block, the traversalterminates.

As mentioned, the search tree 700 is for facilitating the efficientidentification of qualifying rules (rules specified by IP CIDR blocks)that are relevant to a VM or a set of VMs. To use the search tree foridentifying the relevant rules for a VM, some embodiments uses the IPaddress of the VM to query the search tree. The query traverses nodes ofthe search tree and collect all rules that are associated with thetraversed nodes. A node in the search tree will be traversed if (i) itsCIDR block encompasses the queried IP address and (ii) all of itsancestor nodes are also traversed.

FIG. 8 illustrates using the search tree 700 to identify relevant rulesfor several example IP addresses. Each search or query is conducted fora VM based on the VM's IP address. The first example uses the prefixtree 700 for finding the relevant rules for IP address 192.168.101.2.The traversal follows the path of nodes 701, 705, 706, 707, 708, 709, asthe IP address 192.168.101.2 (11000000101010000110010100000010) isparsed into binary substrings for determining the traversal path of thesearch tree. Specifically, the address is parsed into substrings(11000000_10101000_0_1_1001010000_0010) that match the suffix substringsof the traversed nodes 701, 705, 706, 707, 708, 709. Along the way, therules associated with the traversed nodes 705, 708, and 709 (rules 2, 1,5, 7) are collected and identified as the rules that relevant to the IPaddress 192.168.101.2. The traversal ends at the node 709 as it has nochild node. The node 709 is also the last node having a CIDR block thatencompasses the IP address being queried (the CIDR of the node 709 isidentical to the queried IP address 192.168.101.2).

The second example uses the prefix tree 700 for finding the relevantrules for a VM with IP address 192.66.113.9. The traversal follows thepath of nodes 701, 702, and 703, as the IP address 192.66.113.9(11000000010000100111000100001001) is parsed into binary substrings fordetermining the traversal path of the search tree. Specifically, themost significant portions of the IP address (11000000_0100001001_1) isused for matching the suffix substrings of nodes 701, 702, and 703.Along the way, the rules associated with the nodes 702 and 703 (rules 2,5, 8) are collected and identified as the rules that relevant to the IPaddress 192.66.113.9. The traversal ends at the node 703 as it has nochild node. The node 703 is also the last node having a CIDR block thatencompasses the IP address being queried (the subnet 192.66.96.0/19encompasses the IP address 192.66.113.9).

The third example uses the prefix tree 700 for finding the relevantrules for IP address 192.168.128.100. The traversal follows the path ofnodes 701 and 705, as the IP address 192.168.128.100(11000000101010001000000001100100) is parsed into binary substrings fordetermining the traversal path of the search tree. Specifically, themost significant portions of the IP address (11000000_10101000) are usedfor matching the suffix substrings of nodes 701 and 705. Along the way,the rules associated with the node 705 (rule 2) are collected andidentified as the rules that relevant to the IP address 192.168.128.100.The traversal ends at the node 705, because neither child nodes of thenode 705 (706 and 714) can encompass the queried IP address(192.168.128.100 does not fall within 192.168.0.0/17 nor192.168.165.201). This is also because the queried IP address192.168.128.100 is not able to follow the ‘1’ path or the ‘0’ path ofthe node 705, since the suffix substrings of the corresponding childnodes do not match the corresponding bits in the IP address192.168.128.100.

For some embodiments, FIG. 9 conceptually illustrates a process 900 forusing a search tree of firewall rules to identify qualified rulesrelevant to an IP address (non-qualified rules are treated as relevantin some embodiments). In some embodiments, the IP address is that of aVM running on a hypervisor of a host machine, and that the hypervisorperforms the process 900 in order to identify the relevant rules forprotecting the VM as part of its distributed firewall program. In someembodiments, a filter module for the VM performs the process 900 as partof the hypervisor. In some embodiments, the process is performed by asearch structure management module in the hypervisor that receivesqueries for IP addresses and in turn produces relevant rules for queriedIP addresses.

The process 900 starts when it receives (at 910) a query for relevantrules based on an IP address. In some embodiments, the process receivesthe IP address that serves as the basis of the relevant rule query. Theprocess then determines (at 920) if the root node of the searchstructure encompass the queried IP address. If not, the process 900terminates since no other nodes in the search can possibly encompass thequeried IP address. If the root node does encompass the queried IPaddress, the process then sets (at 930) the root node as the currentlytraversed node and proceeds to 940.

At 940, the process collects the rules associated with the currentlytraversed node, if there are any. The process then determines (at 950)if the queried IP address is able to follow the ‘1’ path to the ‘1’child node of the currently traversed node If so, the process proceedsto 955. Otherwise, the process proceeds to 960 to determine if the IPaddress is able to follow the ‘0’ path to the ‘0’ child node of thecurrently traversed node. If so, the process proceeds to 965. Otherwisethe process proceeds to 970.

At 955, the process sets the currently traversed node to the ‘1’ childnode and proceeds to 940. Conversely, at 965, the process sets thecurrently traversed node to the ‘0’ child node and proceeds to 940. Insome embodiments, the queried IP address is able to follow a path to achild node if the suffix substring of the child node matches thecorresponding bits of the queried IP address. When the child node istraversed, it means that the child node's CIDR block encompasses thequeried IP address.

At 970, the process has determined that the queried IP address is notable to traverse to a child node of the current node. In someembodiments, this is because neither child node encompasses the queriedIP address, or because the current node has no child node. In eitherinstance, the current node is the last node to correspond to a CIDRblock that encompasses the queried IP address. The process thereforereports all rules collected during the traversal of the firewall searchstructure as the rules that are relevant or applicable to the queried IPaddress. The process 970 then ends. The querying entity (i.e., thehypervisor or the filter for the VM) then takes the reported rules asthe relevant firewall rules (qualified rules) identified for protectingthe VM.

In some embodiments, a hypervisor constructs and updates the prefix treesearch structure (such as the search tree 700) as it receives firewallconfiguration update messages from the network manager. The constructedtree is then provided to the filters of the VMs as the search structurefor efficient identification of relevant rules. For some embodiments,FIG. 10 conceptually illustrates a process 1000 for constructing andupdating a prefix tree search structure for identifying relevant rulesto a local firewall controller. In some embodiments, the process 1000 isperformed by the hypervisor that performs the local firewall controller.Some embodiments performs the process 1000 continuously to dynamicallykeep its search structure up-to-date such that the filters of the VMswould have access to the latest set of firewall rules.

The process starts when it receives (at 1010) a firewall rule from thenetwork manager (e.g., 310). In some embodiments, the rule is part of afirewall configuration message that is received from the networkmanager. The process then identifies (at 1020) a qualified IP CIDR blockin the received rule from the source address field and the destinationaddress field.

The process then traverses (1030) the firewall rule search tree based onthe rule's CIDR block. In some embodiments, this traversal is based onthe binary string of the received rule's CIDR block (rather than on thebinary string of the IP address of a protected VM as in the process900), i.e., deciding whether to take the ‘0’ path or the ‘1’ path bycomparing the substrings of the child nodes with corresponding bits inthe rule's CIDR block, etc.

The process then determines (at 1040) if it is able to locate a node inthe search structure for the rule's CIDR block from the traversal.Unlike the traversal for finding relevant rules in the process 900 inwhich the search is for identifying nodes with CIDR blocks thatencompass the queried IP address, the traversal here in the process 1000is for finding a node that matches exactly the rule's CIDR block. If theprocess is able to find a node in the search structure that matches therule's CIDR block, the process proceeds to 1050. Otherwise, the processproceeds to 1045.

At 1045, the process adds or inserts a new node into the searchstructure that corresponds to the rule's CIDR block, since the searchstructure has no existing node that corresponds to it. In someembodiments, the process reorganizes the search structure so that thebinary prefix structure of the tree can be maintained. In someembodiments, this reorganization requires adding stub nodes that do notcorrespond to any rules in the firewall, such as the node 706 and 707 inthe search tree 700. After adding the new node for the CIDR block of thereceived rule, the process proceeds to 1050.

At 1050, the process associates the received rule with the node (eitherthe newly added node from the operation 1045 or the located node fromthe operation 1040). The process then determines (at 1060) whether thereare more qualified CIDR block in the received rule. If so, the processreturns to 1020 to either locate an existing node in the searchstructure or to add a new node to the search structure for the otherCIDR block in the rule. Otherwise, the process 1000 terminates, and theconstructed search tree is updated and available for use foridentification of relevant rules.

In some embodiments, the search structure as described in Section II isimplemented at the network manager of the datacenter. The networkmanager constructs and updates the search structure for qualified rulesin its firewall rule database. The search structure is then used toidentify rules relevant to individual VMs, based on queries fromindividual hypervisors for those VMs or on the network manager's ownrecord. The identified relevant rules are then delivered to the hostmachine of those VMs.

III. Computing Device

As mentioned earlier, some embodiments of the invention are implementedby virtualization software or hypervisors running on computing devicesserving as host machines. For some embodiments, FIG. 11 illustrates anexample host machine 1100 that is operating virtualization software1105. The virtualization software 1105 allows the host machine to hostvirtual machines 1111-1114 as well as connecting the virtual machines toa physical network 1190. This physical network 1190 may span one or moredatacenters and include various physical switches and routers.

As illustrated, the host machine 1100 has access to the physical network1190 through a physical NIC (PNIC) 1195. The virtualization software1105 serves as the interface between the hosted VMs 1111-1114 and thephysical NIC 1195 (as well as other physical resources, such asprocessors and memory). Each of the VMs includes a virtual NIC (VNIC)for accessing the network through the virtualization software 1105. EachVNIC in a VM is responsible for exchanging packets between the VM andthe virtualization software 1105. In some embodiments, the VNICs aresoftware abstractions of physical NICs implemented by virtual NICemulators. In some embodiments, the VNIC of a VM also includes afirewall filter for identifying relevant firewall rules and applyingthose firewall rules for filtering packets.

The virtualization software 1105 manages the operations of the VMs1111-1114, and includes several components for managing the access ofthe VMs to the physical network (by implementing the logical networks towhich the VMs connect, in some embodiments). As illustrated, thevirtualization software 1105 includes a physical switching element 1120,a physical routing element 1130, a controller interface 1140, acontext-aware distributed firewall module 1150, and an uplink module1170.

The controller interface 1140 receives control plane messages from acontroller or a cluster of controllers 1160. In some embodiments, thesecontrol plane message includes configuration data for configuring thevarious components of the virtualization software and/or the virtualmachines (such as the physical switching element 1120 and the physicalrouting element 1130). In some embodiments, the control plane messagesalso include messages for firewall configurations, e.g., messages thatinclude updates to the firewall rules stored at the host machine 1100.

The context-aware distributed firewall module 1150 receives the firewallrules update (or the firewall configuration messages) from thecontroller interface 1150. The context-aware distributed firewall module1150 also builds a search structure based on the received firewallrules. The search structure is made accessible to the VMs (or theircorresponding filters in their VNICs) so the relevant rules can beefficiently identified for performing firewall operations as describedabove in Sections I and II.

The physical switching element 1120 (or managed physical switchingelement, MPSE) delivers network data to and from the physical NIC 1195,which interfaces the physical network 1190. The physical switchingelement also includes a number of virtual ports (vPorts) thatcommunicatively interconnects the physical NIC with the VMs 1111-1114,the physical routing element 1130 and the controller interface 1140.Each virtual port is associated with a unique L2 MAC address, in someembodiments. The physical switching element performs L2 link layerpacket forwarding between any two network elements that are connected toits virtual ports. The physical switching element also performs L2 linklayer packet forwarding between any network element connected to any oneof its virtual ports and a reachable L2 network element on the physicalnetwork 1190 (e.g., another VM running on another host).

The physical routing element 1130 (or managed physical routing element,MPRE) performs L3 routing (e.g., by performing L3 IP address to L2 MACaddress resolution) on data packets received from a virtual port on thephysical switching element 1120. In some embodiments, the virtual portthat the physical routing element 1130 is attached to is a sink port.Each routed data packet is then sent back to the physical switchingelement 1120 to be forwarded to its destination according to theresolved L2 MAC address. This destination can be another VM connected toa virtual port on the physical switching element 1120, or a reachable L2network element on the physical network 1190 (e.g., another VM runningon another host, a physical non-virtualized machine, etc.).

The uplink module 1170 relays data between the physical switchingelement 1120 and the physical NIC 1195. In some embodiments, the uplinkmodule 1170 allows the host machine 1100 to serve as a tunnel endpointfor encapsulation overlay networks such as VXLAN and VLANs. VXLAN is anoverlay network encapsulation protocol. An overlay network created byVXLAN encapsulation is sometimes referred to as a VXLAN network, orsimply VXLAN. When a VM on the host 1100 sends a data packet (e.g., anethernet frame) to another VM in the same VXLAN network but on adifferent host, the uplink module 1170 encapsulates the data packetusing the VXLAN network's VNI and network addresses of the VTEP, beforesending the packet to the physical network. The packet is tunneledthrough the physical network (i.e., the encapsulation renders theunderlying packet transparent to the intervening network elements) tothe destination host. The uplink module 1170 also decapsulates incomingVXLAN packets and forwards only the original inner data packet to thedestination VM.

In this document, the term “packet” refers to a collection of bits in aparticular format sent across a network. One of ordinary skill in theart will recognize that the term packet may be used herein to refer tovarious formatted collections of bits that may be sent across a network,such as Ethernet frames, TCP segments, UDP datagrams, IP packets, etc.

This specification refers throughout to computational and networkenvironments that include virtual machines (VMs). However, virtualmachines are merely one example of data compute nodes (DCNs) or datacompute end nodes, also referred to as addressable nodes. DCNs mayinclude non-virtualized physical hosts, virtual machines, containersthat run on top of a host operating system without the need for ahypervisor or separate operating system, and hypervisor kernel networkinterface modules.

VMs, in some embodiments, operate with their own guest operating systemson a host using resources of the host virtualized by virtualizationsoftware (e.g., a hypervisor, virtual machine monitor, etc.). The tenant(i.e., the owner of the VM) can choose which applications to operate ontop of the guest operating system. Some containers, on the other hand,are constructs that run on top of a host operating system without theneed for a hypervisor or separate guest operating system. In someembodiments, the host operating system uses name spaces to isolate thecontainers from each other and therefore provides operating-system levelsegregation of the different groups of applications that operate withindifferent containers. This segregation is akin to the VM segregationthat is offered in hypervisor-virtualized environments that virtualizesystem hardware, and thus can be viewed as a form of virtualization thatisolates different groups of applications that operate in differentcontainers. Such containers are more lightweight than VMs.

Hypervisor kernel network interface modules, in some embodiments, is anon-VM DCN that includes a network stack with a hypervisor kernelnetwork interface and receive/transmit threads. One example of ahypervisor kernel network interface module is the vmknic module that ispart of the ESXi™ hypervisor of VMware, Inc.

One of ordinary skill in the art will recognize that while thespecification refers to VMs, the examples given could be any type ofDCNs, including physical hosts, VMs, non-VM containers, and hypervisorkernel network interface modules. In fact, the example networks couldinclude combinations of different types of DCNs in some embodiments.

IV. Electronic System

Many of the above-described features and applications are implemented assoftware processes that are specified as a set of instructions recordedon a computer readable storage medium (also referred to as computerreadable medium). When these instructions are executed by one or moreprocessing unit(s) (e.g., one or more processors, cores of processors,or other processing units), they cause the processing unit(s) to performthe actions indicated in the instructions. Examples of computer readablemedia include, but are not limited to, CD-ROMs, flash drives, RAM chips,hard drives, EPROMs, etc. The computer readable media does not includecarrier waves and electronic signals passing wirelessly or over wiredconnections.

In this specification, the term “software” is meant to include firmwareresiding in read-only memory or applications stored in magnetic storage,which can be read into memory for processing by a processor. Also, insome embodiments, multiple software inventions can be implemented assub-parts of a larger program while remaining distinct softwareinventions. In some embodiments, multiple software inventions can alsobe implemented as separate programs. Finally, any combination ofseparate programs that together implement a software invention describedhere is within the scope of the invention. In some embodiments, thesoftware programs, when installed to operate on one or more electronicsystems, define one or more specific machine implementations thatexecute and perform the operations of the software programs.

FIG. 12 conceptually illustrates an electronic system 1200 with whichsome embodiments of the invention are implemented. The electronic system1200 can be used to execute any of the control, virtualization, oroperating system applications described above. The electronic system1200 may be a computer (e.g., a desktop computer, personal computer,tablet computer, server computer, mainframe, a blade computer etc.),phone, PDA, or any other sort of electronic device. Such an electronicsystem includes various types of computer readable media and interfacesfor various other types of computer readable media. Electronic system1200 includes a bus 1205, processing unit(s) 1210, a system memory 1225,a read-only memory 1230, a permanent storage device 1235, input devices1240, and output devices 1245.

The bus 1205 collectively represents all system, peripheral, and chipsetbuses that communicatively connect the numerous internal devices of theelectronic system 1200. For instance, the bus 1205 communicativelyconnects the processing unit(s) 1210 with the read-only memory 1230, thesystem memory 1225, and the permanent storage device 1235.

From these various memory units, the processing unit(s) 1210 retrievesinstructions to execute and data to process in order to execute theprocesses of the invention. The processing unit(s) may be a singleprocessor or a multi-core processor in different embodiments.

The read-only-memory (ROM) 1230 stores static data and instructions thatare needed by the processing unit(s) 1210 and other modules of theelectronic system. The permanent storage device 1235, on the other hand,is a read-and-write memory device. This device is a non-volatile memoryunit that stores instructions and data even when the electronic system1200 is off. Some embodiments of the invention use a mass-storage device(such as a magnetic or optical disk and its corresponding disk drive) asthe permanent storage device 1235.

Other embodiments use a removable storage device (such as a floppy disk,flash drive, etc.) as the permanent storage device. Like the permanentstorage device 1235, the system memory 1225 is a read-and-write memorydevice. However, unlike storage device 1235, the system memory is avolatile read-and-write memory, such a random access memory. The systemmemory stores some of the instructions and data that the processor needsat runtime. In some embodiments, the invention's processes are stored inthe system memory 1225, the permanent storage device 1235, and/or theread-only memory 1230. From these various memory units, the processingunit(s) 1210 retrieves instructions to execute and data to process inorder to execute the processes of some embodiments.

The bus 1205 also connects to the input and output devices 1240 and1245. The input devices enable the user to communicate information andselect commands to the electronic system. The input devices 1240 includealphanumeric keyboards and pointing devices (also called “cursor controldevices”). The output devices 1245 display images generated by theelectronic system. The output devices include printers and displaydevices, such as cathode ray tubes (CRT) or liquid crystal displays(LCD). Some embodiments include devices such as a touchscreen thatfunction as both input and output devices.

Finally, as shown in FIG. 12, bus 1205 also couples electronic system1200 to a network 1265 through a network adapter (not shown). In thismanner, the computer can be a part of a network of computers (such as alocal area network (“LAN”), a wide area network (“WAN”), or an Intranet,or a network of networks, such as the Internet. Any or all components ofelectronic system 1200 may be used in conjunction with the invention.

Some embodiments include electronic components, such as microprocessors,storage and memory that store computer program instructions in amachine-readable or computer-readable medium (alternatively referred toas computer-readable storage media, machine-readable media, ormachine-readable storage media). Some examples of such computer-readablemedia include RAM, ROM, read-only compact discs (CD-ROM), recordablecompact discs (CD-R), rewritable compact discs (CD-RW), read-onlydigital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a varietyof recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.),flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.),magnetic and/or solid state hard drives, read-only and recordableBlu-Ray® discs, ultra density optical discs, any other optical ormagnetic media, and floppy disks. The computer-readable media may storea computer program that is executable by at least one processing unitand includes sets of instructions for performing various operations.Examples of computer programs or computer code include machine code,such as is produced by a compiler, and files including higher-level codethat are executed by a computer, an electronic component, or amicroprocessor using an interpreter.

While the above discussion primarily refers to microprocessor ormulti-core processors that execute software, some embodiments areperformed by one or more integrated circuits, such as applicationspecific integrated circuits (ASICs) or field programmable gate arrays(FPGAs). In some embodiments, such integrated circuits executeinstructions that are stored on the circuit itself

As used in this specification, the terms “computer”, “server”,“processor”, and “memory” all refer to electronic or other technologicaldevices. These terms exclude people or groups of people. For thepurposes of the specification, the terms display or displaying meansdisplaying on an electronic device. As used in this specification, theterms “computer readable medium,” “computer readable media,” and“machine readable medium” are entirely restricted to tangible, physicalobjects that store information in a form that is readable by a computer.These terms exclude any wireless signals, wired download signals, andany other ephemeral signals.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of the invention. In addition, a number of the figures(including FIGS. 5, 9, and 10) conceptually illustrate processes. Thespecific operations of these processes may not be performed in the exactorder shown and described. The specific operations may not be performedin one continuous series of operations, and different specificoperations may be performed in different embodiments. Furthermore, theprocess could be implemented using several sub-processes, or as part ofa larger macro process. Thus, one of ordinary skill in the art wouldunderstand that the invention is not to be limited by the foregoingillustrative details, but rather is to be defined by the appendedclaims.

What is claimed is:
 1. A network manager computer operating in adatacenter, the datacenter comprising a plurality of host computersexecuting a plurality of data compute nodes (DCNs), the network managercomputer comprising: a set of processing units; and a non-transitorymachine readable medium storing a program for execution by at least oneprocessing unit in the set of processing units, the program comprisingsets of instructions for: receiving, from a host computer in theplurality of host computers, an identification of a particular DCNexecuting on the host computer; identifying a set of firewall rulesrelevant to the particular DCN for which the network manager computerreceived an identification, wherein the set of firewall rules comprisesfirewall rules identified by the network manager computer from aplurality of firewall rules for protecting a set of DCNs in thedatacenter, the set of relevant firewall rules for the particular DCNcomprising firewall rules that specify either a source or destinationaddress that matches an address of the particular DCN; and sending theidentified set of rules to the host computer, wherein the host computerperforms firewall operations on packets to or from the particular DCN byexamining the set of relevant firewall rules for the particular DCN. 2.The network manager computer of claim 1, wherein the set of relevantfirewall rules for the particular DCN further comprise firewall rulesthat use a classless inter-domain routing (CIDR) block which includesthe address of the particular DCN to specify either a source ordestination address.
 3. The network manager computer of claim 1, whereinthe set of instructions for identifying the set of relevant firewallrules for the particular DCN comprises a set of instructions for using asearch tree structure to identify the relevant rules.
 4. The networkmanager computer of claim 3, wherein the search tree structure comprisesa first node corresponding to a classless inter-domain routing (CIDR)blocks and a second node corresponding to an interne protocol (IP)addresses.
 5. The network manager computer of claim 4, wherein thesearch tree structure is constructed by inserting or locating nodescorresponding to the plurality of firewall rules for protecting the setof DCNs in the datacenter.
 6. The network manager computer of claim 5,wherein the search tree structure is a binary prefix tree.
 7. Thenetwork manager computer of claim 6, wherein the set of instructions forusing a search tree structure to identify the relevant rules comprises aset of instructions for traversing the prefix tree of firewall rules bytraversing nodes according to a binary string of the particular IPaddress associated with the particular DCN.
 8. The network managercomputer of claim 7, wherein the set of instructions for using a searchtree structure to identify the relevant rules comprises a set ofinstructions for identifying the firewall rules associated with thetraversed nodes as firewall rules that are applicable to the particularDCN.
 9. The network manager computer of claim 1, wherein the networkmanager computer does not send firewall rules that are not relevant toDCNs executing on the host computer to the host computer.
 10. For anetwork manager computer operating in a datacenter comprising aplurality of host computers executing a plurality of data compute nodes(DCNs), a method comprising: receiving, from a host computer in theplurality of host computers, an identification of a particular DCNexecuting on the host computer; identifying a set of firewall rulesrelevant to the particular DCN for which the network manager computerreceived an identification, wherein the set of firewall rules comprisesfirewall rules identified by the network manager computer from aplurality of firewall rules for protecting a set of DCNs in thedatacenter, the set of relevant firewall rules for the particular DCNcomprising firewall rules that specify either a source or destinationaddress that matches an address of the particular DCN; and sending theidentified set of rules to the host computer, wherein the host computerperforms firewall operations on packets to or from the particular DCN byexamining the set of relevant firewall rules for the particular DCN. 11.The method of claim 10, wherein the set of relevant firewall rules forthe particular DCN further comprise firewall rules that use a classlessinter-domain routing (CIDR) block which includes the address of theparticular DCN to specify either a source or destination address. 12.The method of claim 10, wherein identifying the set of relevant firewallrules for the particular DCN comprises using a search tree structure toidentify the relevant rules.
 13. The method of claim 12, wherein thesearch tree structure comprises a first node corresponding to aclassless inter-domain routing (CIDR) blocks and a second nodecorresponding to an internet protocol (IP) addresses.
 14. The method ofclaim 13, wherein the search tree structure is constructed by insertingor locating nodes corresponding to the plurality of firewall rules forprotecting the set of DCNs in the datacenter.
 15. The method of claim14, wherein the search tree structure is a binary prefix tree.
 16. Themethod of claim 15, wherein using a search tree structure to identifythe relevant rules comprises traversing the prefix tree of firewallrules by traversing nodes according to a binary string of the particularIP address associated with the particular DCN.
 17. The method of claim16, wherein using a search tree structure to identify the relevant rulescomprises identifying the firewall rules associated with the traversednodes as firewall rules that are applicable to the particular DCN. 18.The method of claim 10, wherein the network manager computer does notsend firewall rules that are not relevant to DCNs executing on the hostcomputer to the host computer.